Ultrasmooth Sub-Nanometer Chemical SiO₂ Surfaces and Enhanced Interface Characteristics via High-pH Fluoride...

Area of Science:

• Materials Science
• Semiconductor Physics
• Surface Chemistry

Background:

• Interface engineering in silicon/high-κ dielectric Metal-Oxide-Semiconductor (MOS) devices is critical for performance.
• Conventional HF-last processes create hydrogen-terminated silicon surfaces prone to interfacial reactions, leading to defects like silicides, silicates, and oxygen vacancies.

Purpose of the Study:

• To develop an ultrasmooth chemical silicon dioxide (SiO2) interlayer for advanced Si/high-κ gate stacks.
• To overcome interfacial reaction challenges associated with conventional surface treatments.

Main Methods:

• Utilized a high-pH fluoride solution (NH4F/(NH4)2SO3/NH4OH) for ultralow, self-limiting etching of silicon surfaces.
• Formed a subnanometer (∼2 monolayers) chemical SiO2 layer via tailored fluoride chemistry.
• Fabricated HfO2 gate stacks on the treated surface and characterized interfacial properties.

Main Results:

• Achieved an atomically smooth SiO2 surface (Rq = 0.06 nm) by eliminating surface features.
• Demonstrated significantly improved interfacial properties, including an 80% reduction in interface trap density and a 60% reduction in fixed oxide charges.
• Observed enhanced breakdown voltages and a shift in carrier transport mechanism.
• Confirmed an atomically smooth and abrupt SiO2/HfO2 interface without element intermixing using HRSTEM and EDS.

Conclusions:

• Established a simple, industry-compatible method for creating atomically smooth SiO2 interlayers.
• Overcame challenges of heterogeneous growth and roughness in chemical SiO2 formation.
• Enabled robust interface control in Si/high-κ gate stacks, providing a scalable pathway for advanced Si CMOS technology.